The principle of using a threaded plug to be retained within the fallopian tube is known from WO 97/12569 which describes a plug in the form of an elongate body having an external thread, which plug, upon rotation, screws itself into the fallopian tube, the plug being self-retaining, and effective when in situ for purposes of sterilisation. Clearly the plug dimensions need to be selected according to the species to be sterilised, with the dual requirement of security against migration which might be caused by muscular tubal peristalsis, yet an ability to remove the plug at a later date should it be required to reverse the sterilisation procedure.
In WO 2007/072004 is described an improved plug less prone to ejection and hence sterilisation failure, by providing a thread with a large root length and a large pitch. The proposal was to produce the plug in implantable grade polyethylene and various dimensions and ratios were advanced for thread forms to meet the practical requirements.
In PCT/GB2009/002450 are described several embodiments of plug proposals intended to provide enhanced resistance to migration and resultant loss of effectiveness.